Mohamed M. Fahmi

Waveguide Antenna Feeders With Integrated Reconfigurable Dual Circular Polarization

Waveguide antenna feeders with reconfigurable circular polarization sense are proposed in this paper. They can be switched between right and left hand circular polarization, without any mechanical rotation between the feeder and the antenna. Two types of feeders are presented. The polarizer works with a single switchable polarization for each state. The dual feeder can work with both polarizations at the same frequency band simultaneously, each one associated with a different rectangular waveguide port. The polarization sense is controlled by metallic posts that block or open the signal paths connecting the rectangular ports with a septum-orthomode polarizer. These posts are automated with piezo-motors integrated in the structure, leading to a very compact layout, reduced size, and practical for applications with diverse switching speed. The proof of concept and the automation are shown with experimental Ku-band prototypes.

Triple-Conductor Combline Resonators for Dual-Band Filters With Enhanced Guard-Band Selectivity

Novel combline resonators and filters with enhanced dual-band characteristics are introduced in this paper. The proposed resonator is made up of three metallic conductors: an inner post, an intermediate conductor, and an enclosure. This structure provides two asynchronous resonant modes that can be used for realizing compact microwave dual-band filters. Such dual-band filters offer the low cost, compact size, and ease of manufacturing features of traditional combline resonator filters, with additional size reduction due to the fact that a single physical cavity provides two electrical resonators. In addition, the new cavity introduces a transmission zero in the guard-bands enhancing the filter selectivity, while keeping a simple and compact inline topology. The design of filters based on this novel resonator is discussed, starting with the resonator circuit model, the coupling scheme, and the complete filter design methodology. Simulations as well as experimental results of a tenth-order (2 × 5) dual-band filter with a measured rejection level in excess of 100 dB in the guard-band are presented to show the concept.

Generalized Multiport Waveguide Switches Based on Multiple Short-Circuit Loads in Power-Divider Junctions

This paper presents a new concept for multiport waveguide switches based on short-circuit loads integrated in power-divider ridge-waveguide junctions. The switching is achieved by means of actuating short and open circuit loads in the waveguide path of a ridge waveguide, eliminating the need of bulky rotors, which are typically used in conventional waveguide switches. A complete class of single-pole N -throw switches (N up to 4) is presented based on this concept. Furthermore, the concept is employed to demonstrate highly compact C-, R-, and T-type waveguide switches by integrating different power-divider junctions in a seamless manner. The T-type case involves three states that provide the maximum flexibility for realizing advanced switch matrices for signal routing. A T-type waveguide switch is built and measured for validating the concept. To our knowledge, this paper marks the first time R- and T-type waveguide switches are demonstrated without the need to use a bulky rotary junction.

Compact ridge waveguide filters using non-resonating nodes

A ridge waveguide filter based on the non-resonating node (NRN) concept is proposed. A new coupling mechanism, suitable for this realization is introduced. The proposed coupling mechanism alleviates the need to use other complicated structures and simplify the design process significantly. Rigorous mode matching method (MMM) is used to model the filter. The filter response is further verified using another numerical technique. A prototype was built and tested. Measurement results agree well with simulation.

Compact Ridge Waveguide Filters With Arbitrarily Placed Transmission Zeros Using Nonresonating Nodes

Compact size ridge waveguide filters based on the nonresonating node concept are introduced to realize transfer functions with arbitrarily placed attenuation poles. Coupling mechanisms, suitable for the new realization are introduced in diverse E -plane and H -plane configurations and with different input-output interfaces. These coupling structures are studied and characterized in detail in order to simplify the design of the proposed filters. Rigorous mode-matching method is used to accelerate the full-wave design of the filter configurations, whose response is also verified using other numerical techniques and experimental data. To validate the proposed novel designs, a prototype has been built and tested. Measurement results agree well with the predicted theoretical simulations.

Compact reconfigurable waveguide circular polarizer

A waveguide circular polarizer with reconfigurable polarization sense is proposed in this paper. The polarizer can be switched between right and left hand circular polarization. The polarization sense is controlled by RF MEMS switches, which commute between two states for allowing or blocking adequately two different signal paths inside the waveguide structure. The polarizer is made up of three building blocks, involving E-plane waveguide MEMS SP2T switch, ridge to waveguide transitions and a septum-orthomode transducer. A switchable Ku-band polarizer prototype is designed and tested as a proof of concept. The experimental performance shows acceptable return losses and axial ratio levels in the 12.7 to 14.8 GHz band (15.3% fractional bandwidth). The proposed structure is compact and is useful for applications that require fast polarization switching.

MEMS multiport switches and switch matrices for satellite applications

Mass and volume of the payload electronics are significant contributors to the overall cost of space systems. Satellite systems rely on switch matrices to provide system redundancy and to enhance capacity by providing flexible interconnectivity. The RF-MEMS technology offers the potential of large reductions in the mass and volume of satellite switch matrices leading to a significant cost reduction of satellite systems. The technology has also the potential of accelerating the development and implementation of new advanced satellite systems. This paper presents various configurations for highly miniature RF MEMS switch matrices. It also presents novel configurations for high power multiport waveguide switches that eliminate the need to use bulky motors.

Compact wide-band ridge waveguide dual-band filters

A compact wide-band, dual-band filter realized in air filled metallic ridge waveguides is proposed. Dual-band filters replace doubly multiplexed filters, thus simplifying the system architecture considerably. The filter is realized in a canonical folded structure layout. Coupling sections that realize strong coupling values required for the wide-band characteristics are achieved by means of transversal sections of ridges connecting the main ridge waveguide resonators. The filter is efficiently modeled using rigorous mode matching method. The filter response is further verified using a commercially available Finite Element Method software. In addition a prototype was built and tested for verification.

Dual-resonance combline resonator for dual-band filters

A novel combline resonator is introduced in this paper for realizing compact microwave dual-band filters. The basic resonator is based on the well-known combline topology, where an additional metallic conductor is introduced for having two TEM modes. The resonant frequencies of the two asynchronous TEM resonant modes are controlled by the length of the two concentric conductors and their spacing. The proposed structure is employed to realize a dual-band filter, where each combline resonator provides one resonant mode per pass-band. The control of the filter parameters, such as pass-band bandwidths and band separation, is addressed. These filters harness the advantages of combline technology for dual-band filters, using the compactness provided by the proposed resonator. A complete design is introduced. Simulations as well as experimental results are presented showing excellent agreement, thus validating the proposed concept.

Compact four-port rectangular waveguide switches based on simple short circuit loads

Four-port rectangular waveguide switches presented in this paper are based on alternating short and open circuit loads in the waveguide path. The switches are made up of four waveguides connected by sections of ridge waveguides where simple short-circuit loads can be activated to control the signal paths. The proposed concept eliminates the need to use bulky rotary mechanisms to provide path switching. The device layout is very simple and is also kept very compact. The concept is presented for C-, R- and T-type switches, based on rigorous full-wave simulations with the model for the short taken into account. An experimental Ku-band prototype for the T-type case (the most complex case involving three states) is built and measured. The experimental performance shows a return loss better than 23 dB from 13 to 14.5 GHz and insertion loss of 0.3–0.4 dB. The isolation of this initial prototype is at least 28 dB in the same band, and it can be increased by improving the short circuit elements.